In comparison with other photographic processes, for example electrophotographic processes and diazo photographic processes, photographic processes in which silver halides are used provide superior photographic characteristics, such as photographic speed and gradation control, and so they have been used in the widest range of applications.
The general field of silver halide photographic processes includes wet processing-type color diffusion transfer methods in which a dye fixing element having a dye fixing layer is laminated with a photosensitive element having a silver halide emulsion layer. In some cases an alkaline processing composition is spread in the form of a layer within this laminate, while in others the laminate is immersed in an alkaline processing fluid.
Recently, methods have been developed in which diffusible dyes are produced or released in correspondence with or in counter-correspondence to the reduction reaction that occurs when a photosensitive silver halide and/or organic silver salt is reduced to silver by thermal development. The diffusible dyes so produced or released are transferred to a dye fixing element. Such methods are disclosed, for example, in U.S. Pat. Nos. 4,463,079, 4,474,867, 4,478,927, 4,507,380, 4,500,626 JP-A-59-168439, -59-17483, and 4,483,914 JP-A-58-149046, JP-A-58-149047, JP-A-59-152440, JP-A-59-154445, JP-A-59-165054, JP-A-59-180548, JP-A-59-168439, JP-A-59-174832, JP-A-59-174833, JP-A-59-174834, JP-A-59-174835, JP-A-62-65038, JP-A-61-23245, and European Patents 210,660A2 and 220,746A2. (The term "JP-A" as used herein signifies an "unexamined published Japanese patent application".)
However, there are problems associated with the above methods of image formation in that the reflection density in the white base parts is initially high after image formation, and it tends to increase on ageing.